1. Field of the Invention
The present invention deals with photographic silver halide elements prepared by chemical sensitization, and particularly with new compounds and metal complexes for this purpose.
2. Description of the Prior Art
A wide variety of chemical compounds and complexes, known as chemical sensitizers, react chemically with photographic silver halide grains. While these grains exhibit natural sensitivity to light, chemical sensitization allows the sensitivity to be considerably enhanced. If the purpose is to produce direct positive emulsions the grains are reacted until they are fogged.
Known prior art sensitizing and fogging agents include organic and inorganic sulfur compounds, gold and other heavy metal complexes, amines, and boranes. Bigelow in U.S. Pat. No. 3,930,867 discloses macrocyclic polyamines, salts and metal chelates as sensitizers for silver halide emulsions. Structures for several prior art polyamine sensitizers, some of which are disclosed in Bigelow, are as follows: ##STR1##
The present invention provides a class of polyamine sensitizers for silver halide emulsions which are somewhat analogous in structure to prior art polyamine sensitizers, but have increased emulsion speed, which can be translated into reduced silver coating weight.